A 301 redirect is a permanent redirect link from one server to another. When a 301 redirect occurs correctly, the user will never know that a server switch has occurred.
A 301 redirect is typically used when a site has been moved to a new domain. If the web browser user types in the old address they will be redirected to the new address automatically.
A 301 redirect is also used if a web browser user mis-types a URL. For example, "gogle.com" and "gooogle.com" will be redirected to "google.com" Organizations will register commonly "mis-spelled" domains and re-direct them to the "correct" location.